NASA Cassini Significant Events 12/19/2012 - 12/25/2012

Cassini is orbiting Saturn with a period of 13.3 days and inclined 53 degrees from the equatorial plane. The most recent spacecraft tracking and telemetry data were collected on Dec. 26 by the Deep Space Network's 70 meter Station 14 at Goldstone, California. Except for some science instrument issues described in previous reports, the spacecraft continues to be in an excellent state of health with all of its subsystems operating normally. Information on the present position of the Cassini spacecraft may be found on the "Present Position" page at:http://saturn.jpl.nasa.gov/mission/presentposition/ .

Transits of Venus (when Venus passes in front of the Sun) are rare when seen from Earth. They come in pairs eight years apart, separated by more than a century. These rare events have been important in the history of astronomy because they permitted observers to mathematically unlock the distance from Earth to the Sun, and thus the size of our solar system. Cassini made history on Friday by observing the first transit of Venus from the vicinity of another planet. Such an observation is no longer important for measuring our own solar system; instead it may help scientists prepare to detect chemical compounds in the planetary systems of distant stars. More information on Cassini's unique observation may be found here: http://go.usa.gov/gH7A

Wednesday, Dec. 19 (DOY 354)

The Imaging Science Subsystem (ISS) carried out an observation of the F ring to make a movie nearly twelve hours in length, with the Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) also taking data. Then ISS watched the B ring for 13.5 hours, making a movie in search of "spoke" features; CIRS and the Ultraviolet Imaging Spectrograph (UVIS) rode along. An example of a spoke may be seen here: http://saturn.jpl.nasa.gov/video/videodetails/?videoID=186

ISS made a 6.5 hour observation of the irregular moon Surtur today. This six-kilometer diameter rock is in a retrograde, highly inclined and highly eccentric orbit about Saturn. ISS repeated the observation on Monday for fourteen hours.

Targeted encounters generally require firing Cassini's main rocket engine or the smaller Reaction Control Subsystem thrusters, steering for a specific flyby point. Non-targeted encounters are more casual ones that may happen along the way. Today's encounter with Rhea was of the latter kind. CIRS, UVIS and VIMS observed the south pole on approach to the daytime hemisphere. Next the radar instrument performed scatterometry and radiometry scans of Rhea, then ISS led the optical remote-sensing observations through a closest approach of 22,872 kilometers.

Sunday, Dec. 23 (DOY 358)

ISS turned to Enceladus for observations of its plume, and then radar turned to Dione for scatterometry and radiometry measurements, after which ISS carried out global color imaging of Dione. UVIS was given two and a half hours for a calibration, observing the blue star Alpha Virginis, also known as Spica.

A 34 meter Deep Space Network (DSN) station in Australia participated in an operational readiness test, preparing for the Radio Science Saturn occultation experiment coming up early next month.

Monday, Dec. 24 (DOY 359)

The DSN carried out two-way communications with Cassini on six days this week, using 70 meter and 34 meter diameter antennas at each of its complexes: Madrid, Spain, Canberra Australia, and Goldstone, California. Cassini carried out three Reaction Wheel Assembly bias maneuvers to adjust wheel speeds while thrusters stabilized the spacecraft. The DSN tracked one of these maneuvers, providing realtime Doppler data showing the thrusters' effects on the spacecraft's trajectory.

ISS created a 10.5 hour movie of the streamer-channel feature raised in the F ring by Prometheus's apoapsis passage, then it performed an observation in the satellite orbit campaign, looking at small satellites near Saturn. Following that, ISS, CIRS and VIMS made observations in the Titan monitoring campaign from 2.2 million kilometers away. Finally, CIRS began a 16 hour observation of Saturn, measuring oxygen compounds (H2O and CO2) in the stratosphere.